It has been recognized for some time that proteinproviding feed materials which are subject to digestion in the rumen are thereby deleteriously altered in their feeding value. It has been proposed that ideally the protein component of the ruminant feed should be "protected" against being solubilized or metabolized in the rumen, passing therethrough in substantially undegraded form, while remaining digestable and metabolizable in the post-rumen digestive system of the cattle or sheep. The development of a practical way for applying this concept to ruminant nutrition has proven difficult. U.S. Pat. No. 3,619,200 proposes the application to the vegetable meal or other proteinaceous ruminant feed material of a rumen resistant coating. The purpose of the coating is to protect the proteinaceous feed from microbial attack in the rumen while decomposing and permitting digestion of the feed within the abomasum and small intestine.
It is also known that the solubility of protein in ruminant feed materials can be reduced by treating the feed materials with tannin, formaldehyde, or other aldehydes. In addition, a reduction in protein solubility can be obtained by heating the protein. These procedures are summarized with literature references thereto in U.S. Pat. No. 4,186,213. Feed materials which may be treated by one or more of these procedures to reduce the solubility of the protein in the rumen and to protect against rumen destruction are disclosed as including various vegetable meals.
With reference to feeding value lost by rumen destruction, soybean meal has a relatively low protein efficiency value. See Klopfenstein, Feedstuffs, July, 1981, 23-24. Since soybean meal is one of the major protein-containing feed materials used with ruminants, it is particularly desirable to provide a commercially practical means for protecting soybean meal against rumen destruction while leaving the protein thereof subject to post-ruminal digestion and metabolism. For large scale commercial use such a method must be simple, efficient, and of relatively low cost. Such a method should be capable of being integrated with present commercial processing of soybeans to produce soybean feed materials.
Other prior art references of interest are Hudson et al. (1970), J. Anim. Sci., 30:609-613; Tagari et al. (1962), Brit. J. Nutr., 16:237-243; Anderson U.S. Pat. No. 3,463,858 (1969); Emery et al. U.S. Pat. No. 2,295,643 (1942); and Ashmead U.S. Pat. No. 4,172,072 (1979).
Hudson et al. describe an experimental comparison in lambs of postruminal nitrogen utilization of commercial soybean meal (72% N soluble) with meal heated 4 hours at 140.degree. C. (35% N soluble). The results suggest that the heated meal was degraded at a slower rate by ruminal microorganism.
Tagari et al. compared solvent extracted soybean meals of different heat exposures. These included room temperature solvent removal, solvent removal at 80.degree. C. for 10 minutes, and commercial toasted meal steamed at 120.degree. C. for 15 minutes. The meals were fed to rams and rumen liquor samples were tested. Artificial rumen comparisons for ammonia liberation were also made. It was concluded that results clearly showed "that the main factor determining the different efficiencies of process to non-process soybean meals is their different solubility in rumen liquor." It was also observed that changes in solubility caused by different heat treatments of soybean meal are relatively large in comparison with other meals.
Anderson discloses a procedure for preparing a growth factor for feeding domestic animals and poultry. A zinc salt in aqueous solution such as zinc chloride or zinc sulfate is reacted with free amino acids in a proteinaceous feed material. The reaction is carried out in an aqueous solution at a temperature of 60.degree.-70.degree. C. (140.degree.-158.degree. F.) and a pH of 3.5, which pH is said to be achieved automatically with ZnCl.sub.2, an adjustment of pH with HCl being used with other zinc salts. The reaction mixture is dried to a moisture content of 2-8%, and mixed with the feed ration. There is no reference to the feeding of ruminants, or to rumen protection of protein.
Emery et al. describes a process in which mineral compounds including zinc and other polyvalent metal oxides, hydroxides, and salts are reacted with proteinaceous feed materials in the presence of water and a protein splitting acid such as H.sub.2 PO.sub.4, HCl, or H.sub.2 SO.sub.4. The reacted mixture is dried by heating in air. Soybean meal is indicated as the preferred feed material and zinc is among the metals referred to for use in the form of oxides, hydroxides, or carbonates. Other salts, such as cobalt, are indicated as being used in the form of chlorides or sulfates. The examples illustrate the reaction of large amounts of the metal compounds with soybean meal (Ex. I, 35% and Ex. III, 17%, based on the meal). There is no reference in this patent to either rumen protection or nutritional value.
Ashmead proposes the use of metal proteinates for supplying mineral deficiencies in humans and animals. The proteinates are prepared by reacting bivalent metal salts at an alkaline pH with free amino acids of enzyme-hydrolyzed proteins.
Zinc compounds of limited water solubility such as zinc oxide and zinc carbonate have heretofore been employed for supplying micronutrient zinc to ruminants. The utilization of zinc as a micronutrient is post-ruminal and the amount of zinc required as a micronutrient for cattle is quite small, typically about 50 to 150 ppm based on the total daily diet. Small amounts of zinc are present in cattle feed materials, such as proteinaceous oil seed meals, ranging from 25 to 150 pm. Lease and Williams, Poultry Science, 46:233-241, Table 1 at 2364 (1967).
The toxicity of high levels of zinc oxide has been studied: Miller et al., J. Dairy Sci., 48:450-453 (1966); Ott et al. J. Anim. Sci., 25:414-438 (1966). These investigators tested zinc oxide in admixture with ruminant feed materials in amounts greater than micronutrient levels. Miller et al. fed amounts of zinc to lactating dairy cattle up to 2000 ppm based on the feed concentrate (1279 ppm for total diet). No beneficial effect on milk production was observed by the increased ZnO in the diet. Ott et al. fed lambs pelleted rations containing from 0.5 to 4.0 grams of zinc per kilogram of diet, and beef cattle from 1.0 to 3.0 grams zinc per kilogram of diet. These rations included soybean meal. Lambs receiving 0.5 to 1.0 grams zinc gained somewhat faster than the controls, but no increase in rate of weight gain was observed for the beef cattle. Ott et al. reported that steers were less adversely affected by high levels of zinc than heifers.